Chemoprevention of Tamoxifen-induced Endometrial cancer by black cohosh and red clover Breast cancer is the most common cancer in women. The selective estrogen receptor modulator tamoxifen, which antagonizes estrogen in breast tissue, is efficacious in the treatment and prevention of breast cancer. In tamoxifen treated patients, botanical dietary supplements such as red clover and black cohosh extracts are frequently used for the alleviation of tamoxifen related menopausal symptoms. Very few studies about the modifying effects of these botanicals on tamoxifen's safety and efficacy have been reported. Tamoxifen's major side effect is an enhanced endometrial cancer risk. Tamoxifen's ER1 mediated uterotrophic activity and its reactive metabolites are believed to be responsible for this effect. Black cohosh and red clover contain anti-oxidative, anti-proliferative, anti-inflammatory, and detoxification enzyme inducing compounds, which could inhibit the initiation or retard the promotion and progression of cancerous cells. The central hypothesis of this project is that black cohosh and red clover reduce the carcinogenic effects of tamoxifen on the endometrium by inhibition of cell proliferation (Aim I) and through enhancing detoxification pathways (Aim 2). To support this hypothesis we propose the following specific aims: 1. What is the effect of red clover or black cohosh on tamoxifen-stimulated endometrial cancer? Recent data suggest that black cohosh and red clover can attenuate tamoxifen-stimulated endometrial cancer growth by inhibiting cell proliferation. We will measure the influence of these botanicals on tamoxifen stimulated endometrial tumor growth in ovariectomized athymic nude mice, an established endometrial cancer model for studying estrogenic influences. The mechanism of interaction will be examined by analyzing the expression of pro-proliferative genes and proteins important for tamoxifen mediated tumor promotion in vivo and in vitro. To further identify active compounds, we will examine the anti-proliferative effect of isolated compounds in endometrial cancer cells and in an immature rat model. 2. What is the effect of black cohosh or red clover on detoxification pathways of reactive tamoxifen metabolites? Our data indicate that both botanical upregulate the cellular antioxidative response machinery, thus reducing the carcinogenic effect of tamoxifen's reactive metabolites. We will study the ability of these botanicals to induce the detoxification enzymes, quinone reductase and glutathione-S-transferase, in the uterus and liver of adult rats. We will also analyze whether black cohosh and red clover prevent tamoxifen induced oxidative stress in these animals. Additionally, we will examine the effect of the botanicals on tamoxifen's metabolism to active or reactive metabolites in the blood. To elucidate the compounds responsible for the various effects, isolated constituents will be assayed in vitro. The completion of these specific aims will provide an overall picture of the effect of these botanicals and purified compounds on the efficacy of tamoxifen and on tamoxifen induced endometrial cancer, which is of importance considering the increasing number of breast cancer survivors and women at high risk undergoing tamoxifen treatment. PUBLIC HEALTH RELEVANCE: The selective estrogen receptor modulator, tamoxifen, is very effective in treatment and prevention of breast cancer;however, it causes menopausal symptoms and has carcinogenic effects on the endometrium. We hypothesize that red clover and black cohosh, both frequently used for the alleviation of menopausal symptoms, will reduce tamoxifen-induced endometrial cancer due to their cancer chemopreventive properties.